Structure and Development of Viruses as Observed in the Electron Microscope

Abstract

Stages in the direct penetration of adenovirus through the cell membrane are illustrated. Phagocytosis with rupture of the vacuole and release of virus into the cytoplasm may also account for entry of some particles. Uncoating by digestion within phagosomes was not observed. Rather, alteration of capsid and core occurred to virions free in the cytoplasm. Nucleoprotein released from virus close to the nucleus was transported to the nuclear matrix by a unique mechanism. These events were not prevented by puromycin and hence were not dependent upon the synthesis of new enzymes. They were, however, energy-dependent.

Early events in cell-animal virus interactions

“…Such rarely encountered images were found in samples taken 3 to 6 h after inoculation, when replication was already in progress. x pass directly through the plasma membrane into the cytoplasm of the host (141). In this study, paucity of images purporting to demonstrate such a phenomenon is explained by presuming that the process is unusually rapid or uncommon.…”

“…5). Incidentally, such coated membranes deserve further attention in the future, for they are regions where often the inoculum is both attached and engulfed, as has been observed with several animal agents including influenza, adenovirus, and VSV (36,141,185).…”

“…In addition to viropexis fusion between envelopes of the inoculum and the plasma membrane as a process for incorporating directly the nucleoprotein moiety must now be recognized. Among the rarely proposed additional routes for ingress are (i) the development of breaks or dissolution of the plasma membrane (135) and (ii) direct transgress whereby intact or quasi-intact virions "melt their way" through the membrane into the cell proper (56,141). The up-to-date electron microscopy information on penetration has been summarized in Table 1 and will now be considered according to the respective virus types.…”

How non-enveloped viruses hijack host machineries to cause infection

“…2, step 3). This idea is based on early negative-stain electron microscopy (EM) and fluorescence imaging studies (Greber et al, 1993; Morgan et al, 1969). In addition to these descriptive reports, functional analyses using inhibitors of endosomal acidification supported this idea (FitzGerald et al, 1983).…”

Disparate Entry of Adenoviruses Dictates Differential Innate Immune Responses on the Ocular Surface

“…Clathrin-mediated endocytosis is the best elucidated route for viral entry, including for adenovirus [64,68,69,70,71]. This entry process involves the internalization of virions into a double membrane coated pit with triskelion-shaped clathrin proteins, which collectively interact to form a polyhedral lattice surrounding the endocytosed vesicle [64,72,73].…”